Plasma display panel

ABSTRACT

A plasma display panel (PDP) includes: a front substrate; a rear substrate disposed in opposition to the front substrate; first barrier ribs disposed between the front substrate and the rear substrate, defining discharge cells with the front substrate and the rear substrate, and formed of a dielectric material; front discharge electrodes disposed inside the first barrier ribs so as to surround the discharge cells; rear discharge electrodes disposed inside the first barrier ribs so as to surround the discharge cells, and spaced apart from the front discharge electrodes; phosphor layers disposed in the discharge cells; and a discharge gas deposited in the discharge cells. With respect to a longitudinal sectional view of the first barrier ribs, a virtual horizontal axis which extends from a lowermost portion of each of the rear discharge electrodes and is parallel to the front substrate intersects a lateral surface of the first barrier ribs at a certain position. An angle between a tangent line at the intersection of the horizontal axis and a lateral surface of the first barrier ribs, on one hand, and a virtual vertical axis orthogonal to the horizontal axis, on the other hand, ranges from 4° to 17°.

CLAIM OF PRIORITY

This application makes reference to, incorporates the same herein, andclaims all benefits accruing under 35 U.S.C. §119 from an applicationfor PLASMA DISPLAY PANEL earlier filed in the Korean IntellectualProperty Office on 20 Apr. 2004 and there duly assigned Serial No.10-2004-0027158.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a plasma display panel (PDP) and, moreparticularly, to a PDP with a new structure.

2. Related Art

A device adopting a plasma display panel (PDP) has not only a largescreen but also some excellent characteristics, such as high definition(HD), ultra-thin thickness, light weight, and wide viewing angle. Also,in comparison with other flat panel displays, the device including thePDP can be manufactured in a simple process can be easily fabricated ina large size, so that it has attracted much attention as the nextgeneration of flat panel devices.

A PDP can be classified into a direct current (DC) PDP, an alternatingcurrent (AC) PDP, and a hybrid PDP according to the type of dischargevoltage applied to it. The PDP can also be divided into an opposingdischarge type PDP and a surface discharge type PDP according to thedischarge structure. In recent years, an AC surface discharge typetriode PDP has typically been used.

In the PDP, a considerable amount (about 40%) of visible rays emittedfrom phosphor layers are absorbed in scan electrodes, common electrodes,bus electrodes, a dielectric layer covering the electrodes, and amagnesium oxide (MgO) protective layer, which are disposed on a bottomsurface of a front substrate. Thus, luminous efficiency is low.

Furthermore, when the surface discharge type triode PDP displays thesame image for a long period of time, the phosphor layers areion-sputtered due to charged particles of the discharge gas, thuscausing a permanent image sticking.

SUMMARY OF THE INVENTION

The present invention provides a plasma display panel (PDP) withimproved luminous efficiency.

According to an aspect of the present invention, there is provided a PDPincluding: a front substrate; a rear substrate disposed opposite to thefront substrate; first barrier ribs which are disposed between the frontsubstrate and the rear substrate for defining discharge cells with thefront substrate and the rear substrate, and which are formed of adielectric material; front discharge electrodes disposed inside thefirst barrier ribs so as to surround the discharge cells; rear dischargeelectrodes disposed inside the first barrier ribs so as to surround thedischarge cells and spaced apart from the front discharge electrodes;phosphor layers disposed in the discharge cells; and a discharge gaswhich fills the discharge cells. From a longitudinal sectional view ofthe first barrier ribs, a virtual horizontal axis, which extends from alowermost portion of each of the rear discharge electrodes and which isparallel to the front substrate, intersects a lateral surface of thefirst barrier ribs at a certain position. An angle between a tangentline at the intersection of the horizontal axis and the lateral surfaceof the first barrier ribs, on one hand, and a virtual vertical axisorthogonal to the horizontal axis, on the other hand, ranges from 4° to17°.

The front discharge electrodes may extend in a given direction, and therear discharge electrodes may extend in a direction which crosses thegiven direction in which the front discharge electrodes extend. Also,the front discharge electrodes and the rear discharge electrodes mayextend in directions parallel to each other. The PDP of the presentinvention may further include address electrodes which extend in adirection which crosses the direction in which the front dischargeelectrodes and the rear discharge electrodes extend.

According to the present invention, an MgO protective layer is formed toa uniform thickness on the lateral surface of the first barrier rib, anda sustain voltage margin is sufficient. As a result, uniform plasmadischarge occurs, thus improving discharge properties and luminousefficiency.

Also, surface discharge can be induced from all of the lateral surfacesof a discharge space so that the discharge surface can be greatlyenlarged.

Furthermore, as discharge occurs from the lateral surfaces of thedischarge cells and spreads toward the centers of the discharge cells,the discharge region notably increases, thus enabling efficientutilization of the entirety of the discharge cells. Accordingly, the PDPcan be driven at a low voltage so that luminous efficiency isconsiderably enhanced.

In addition, because the PDP can be driven at a low voltage, even if ahigh-concentration Xe gas is used as a discharge gas, luminousefficiency improves.

Moreover, since an electric field caused by a voltage applied to thedischarge electrode formed on the lateral surface of the discharge spacecrowds plasma into the center of the discharge space, even if dischargeoccurs for a long period of time, collision of generated ions with thephosphor layers due to the electric field is prevented. This inhibitsthe phosphor layers from being ion-sputtered, with the result that nopermanent image sticking is caused.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which likereference symbols indicate the same or similar components, wherein:

FIG. 1 is an exploded perspective view of a plasma display panel (PDP);

FIG. 2 is a cutaway exploded perspective view of a PDP according to anexemplary embodiment of the present invention;

FIG. 3 is a cross sectional view taken along lines III—III of FIG. 2;

FIG. 4 is a perspective view of discharge cells and electrodes shown inFIG. 2;

FIG. 5 is a magnified cross sectional view of a first barrier rib and anMgO layer shown in FIG. 2;

FIG. 6 is a graph of a sustain voltage margin with respect to a tangentangle;

FIG. 7 is a graph of a thickness deviation of the MgO layer with respectto a tangent angle;

FIG. 8 is a magnified longitudinal sectional view of the first barrierribs when a tangent angle is more than 0°; and

FIG. 9 is a magnified longitudinal sectional view of the first barrierribs when a tangent angle is less than 0°.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is an exploded perspective view of a plasma display panel (PDP),and in particular a surface discharge type triode PDP. In the PDP 100 ofFIG. 1, a considerable amount (about 40%) of visible rays emitted fromphosphor layers 110 are absorbed in scan electrodes 106, commonelectrodes 107, bus electrodes 108, a dielectric layer 109 covering theelectrodes 106, 107 and 108, and an MgO protective layer 111, which aredisposed on a bottom surface of a front substrate 101. Thus, luminousefficiency is low.

Furthermore, when the surface discharge type triode PDP 100 displays thesame image for a long period of time, the phosphor layers 110 areion-sputtered due to charged particles of the discharge gas, thuscausing permanent image sticking.

A plasma display panel (PDP) according to an exemplary embodiment of thepresent invention will now be described with reference to FIGS. 2through 7.

FIG. 2 is a cutaway exploded perspective view of a PDP according to anexemplary embodiment of the present invention, while FIG. 3 is a crosssectional view taken along lines III—III of FIG. 2, and FIG. 4 is aperspective view of discharge cells and electrodes shown in FIG. 2.

Referring to FIGS. 2 and 3, PDP 200 includes a front substrate 201, arear substrate 202, address electrodes 203, a dielectric layer 204,first barrier ribs 208, second barrier ribs 205, front dischargeelectrodes 206, rear discharge electrodes 207, MgO layers 209 andphosphor layers 210. The rear substrate 202 is disposed parallel andopposite to the front substrate 201. The first barrier ribs 208 aredisposed between the front substrate 201 and the rear substrate 202,they define discharge cells 220 with the front and rear substrate 201and 202, and they are formed of a dielectric material. The frontdischarge electrodes 206 are disposed inside the first barrier ribs 208so as to surround the discharge cells 220. The rear discharge electrodes207 are disposed inside the first barrier ribs 208 so as to surround thedischarge cells 220, and they are spaced apart from the front dischargeelectrodes 206. The phosphor layers 210 are disposed in the dischargecells 220, which are filled with a discharge gas (not shown).

In the exemplary embodiment of the present invention, since visible raysfrom the discharge cells 220 are transmitted through the front substrate201 and then externally emitted, the front substrate 201 is formed of amaterial, such as glass, having good transmissivity. The front substrate201 of the present invention transmits visible rays in the forwarddirection much better because it does not include scan electrodes,common electrodes, and bus electrodes, as compared with the frontsubstrate of the PDP 100. Therefore, if an image is embodied at theordinary level of luminance, the scan electrodes 106, common electrodes107 and bus electrodes 108 are driven at a relatively low voltage sothat luminous efficiency improves.

The first barrier ribs 208 disposed under the front substrate 201 definethe discharge cells 220, each of which corresponds to red, green or blueemitting sub-pixels that form one pixel. Also, the first barrier ribs208 prevent generation of a misdischarge between the discharge cells220. As shown in FIG. 4, the first barrier ribs 208 are formed such thatthe discharge cells 220 are partitioned in a rectangular matrix shape.

The first barrier ribs 208 prevent an electrical short between the frontdischarge electrodes 206 and the rear discharge electrodes 207 andinhibit charged particles from directly colliding with the frontdischarge electrode 206 and the rear discharge electrode 207, anddamaging the same. The first barrier ribs 208 may be formed of adielectric material, such as PbO, B₂O₃, or SiO₂, which can accumulatewall charge by inducing charged particles.

As shown in FIG. 4, the front discharge electrodes 206 and the reardischarge electrodes 207 are disposed inside the first barrier ribs 208such that the discharge cells 220 are surrounded. The front dischargeelectrode 206 and rear discharge electrode 207 are formed of aconductive metal, such as Al or Cu. Also, the front discharge electrodes206 and rear discharge electrodes 207 are spaced apart from each other,and extend parallel to each other in a vertical direction relative tothe front substrate 201. In this case, the front discharge electrodes206 and the rear discharge electrodes 207 are symmetric with respect toa virtual surface which is parallel to the front substrate 201.

Also, when the distance between a scan electrode and an addresselectrode is small, address discharge is efficiently provoked.Accordingly, in the exemplary embodiment of the present invention, therear discharge electrodes 207 act as scan electrodes because they areclose to the address electrodes 203, while the front dischargeelectrodes 206 act as common electrodes. However, even if addresselectrodes are not used, address discharge between the front dischargeelectrodes 206 and rear discharge electrodes 207 is enabled. Thus, thepresent invention is not limited to PDPs which include addresselectrodes. Although not shown in the drawings, if no address electrodesare formed, the rear discharge electrodes 207 extend in a direction soas to cross the direction in which the front discharge electrodes 206extend.

The rear substrate 202 supports the address electrodes 203 and thedielectric layer 204, and is typically formed of glass as the mainelement.

The address electrodes 203 are disposed on a front surface of the rearsubstrate 202. The address electrodes 203 extend across the frontdischarge electrodes 206 and the rear discharge electrodes 207.

The address electrodes 203 are used to generate address discharge, whichfacilitates sustain discharge between the front discharge electrodes 206and the rear discharge electrodes 207. More specifically, the addresselectrodes 203 aid in lowering the voltage at which sustain dischargebegins. Address discharge refers to discharge induced between a scanelectrode and an address electrode. Once the address discharge ends,positive ions are accumulated in the scan electrode, and electrons areaccumulated in a common electrode, thereby facilitating sustaindischarge between the scan electrode and the common electrode.

The dielectric layer 204 in which the address electrodes 203 are buriedis formed of a dielectric material, such as PbO, B₂O₃, or SiO₂, whichprevents positive ions or electrons from colliding with and damaging theaddress electrodes 203 during discharge, and also induces charges.

The PDP 200 of the present invention may further include second barrierribs 205, which are disposed between the first barrier ribs 208 and therear substrate 202, and which define the discharge cells 220 togetherwith the first barrier ribs 208. Although FIG. 2 illustrates that thefirst barrier ribs 208 and the second barrier ribs 205 are partitionedin a matrix shape, the present invention is not limited thereto. As longas it is possible to form a plurality of discharge spaces, the firstbarrier ribs 208 and second barrier ribs 205 may have a variety ofpatterns. For example, the first barrier ribs 208 and second barrierribs 205 may have not only open patterns, such as stripes, but alsoclosed patterns, such as waffles, matrixes, and deltas. Also, inaddition to the rectangular cross sections as in the present embodiment,closed barrier ribs may be formed such that the cross sections ofdischarge spaces are polygonal (e.g., triangular or pentagonal),circular, or elliptical. In the present embodiment of the presentinvention, the first barrier ribs 208 and the second barrier ribs 205have the same shape, but may have different shapes.

As shown in FIG. 4, the phosphor layers 210 substantially form a planartop surface with the second barrier ribs 205. Preferably, the phosphorlayers 210 are coated on the lateral surfaces of the second barrier ribs205, and on the rear substrate 202 between the second barrier ribs 205.

The phosphor layers 210 contain elements that absorb ultraviolet raysand emit visible rays. Namely, phosphor layers in a red emittingsub-pixel contain a fluorescent material such as Y(V,P)O4:Eu, phosphorlayers in a green emitting sub-pixel contain a fluorescent material suchas Zn₂SiO₄:Mn or YBO₃:Tb, and phosphor layers in a blue emittingsub-pixel contain a fluorescent material such as BAM:Eu.

A discharge gas, for example, Ne, Xe, or a mixture thereof, is injectedinto the discharge cells 220, and the discharge cells 220 are sealed. Inthe present invention, because the discharge surface can increase anddischarge regions can be enlarged, the amount of generated plasmaincreases, thus enabling a low-voltage driving of the PDP 200.Accordingly, even if high-concentration Xe gas is used as a dischargegas, the PDP 200 can be driven at a low voltage so that luminousefficiency is greatly enhanced. This solves the problems of a PDP whichcannot be driven at a low voltage when a high-concentration Xe gas isused as a discharge gas.

At least the lateral surfaces of the first barrier rib 208 may becovered by the protective layer 209, which is formed of MgO. The MgOlayer 209 is not an indispensable element, but it prevents chargedparticles from colliding with and damaging the first barrier ribs 208formed of a dielectric material, and it also emits a lot of secondaryelectrons during discharge.

The MgO layer 209 is typically formed using deposition methods after thefirst barrier ribs 208 are formed. It is possible to use non-vacuumdeposition techniques, such as spray pyrolysis, but the MgO layer 209 isgenerally obtained by methods using MgO as a source. For instance, anMgO source is dissolved using e-beam methods and evaporated, or MgO issputtered and deposited.

However, if the MgO layer 209 is deposited by emitting an MgO gas towardthe front substrate 201, since lateral surfaces 208 a of the firstbarrier ribs 208 are sloped downward as shown in FIG. 3, it is highlyfeasible that the MgO layer 209 formed on the lateral surfaces 208 a ofthe first barrier ribs 208 have a non-uniform thickness. Also, becausethe MgO may flow down the slopes of the lateral surfaces 208 of thefirst barrier ribs 208, it is harder to obtain a uniform thickness ofthe MgO layer 209. Therefore, in order to form the MgO layer 209 with auniform thickness, the lateral surfaces 208 a of the first barrier ribs208 should be appropriately formed.

In particular, portions of the lateral surfaces 208 a, on whichconcentrated discharge from the front discharge electrodes 206 and reardischarge electrodes 207 are projected, greatly affect the thickness ofthe MgO layer 209. If the gradient of the lateral surface 308 a is toohigh as shown in FIG. 8, a difference occurs between the depths h₁ andh₂ of portions of a first barrier rib 308 that covers a front dischargeelectrode 306 and a rear discharge electrode 307, respectively. As aresult, the amount of wall charge accumulated on both of the electrodes306 and 307 become different during discharge, thus inducing non-uniformdischarge.

However, if the gradient of the lateral surface 408 a is too low, i.e.,a minus value, as shown in FIG. 9, since the lateral surface 408 as of afirst barrier rib 408 is blocked by a bottom surface 408 b of the firstbarrier rib 408, no MgO layer is formed on the lateral surface 408 a.Even if the MgO layer 209 is deposited on the lateral surface 408 a, theMgO flow is downward so that it cannot be formed to a uniform thickness.

Accordingly, as described above, in order to deposit the MgO layer 209with a uniform thickness, the shape of the first barrier rib 208 shouldbe determined in consideration of positions of the front dischargeelectrodes 206 and rear discharge electrodes 207, such that the lateralsurfaces 208 a have an appropriate gradient.

The present invention obtains such an appropriate shape of the lateralsurface 208 a as to render uniform the thickness of the MgO layer 209based on the rear discharge electrodes 207 on which discharge isconcentrated, and the first barrier ribs 208 are formed at a relativelyhigh gradient. Hereinafter, a lateral line 208 b (FIG. 5) of the lateralsurface 208 a will be chiefly observed and described.

FIG. 5 is a magnified longitudinal sectional view of a first barrier riband an MgO layer shown in FIG. 2.

Referring to FIG. 5, from the longitudinal sectional view of the firstbarrier rib 208, a virtual horizontal axis (x-axis), which extends froma lowermost portion 207 a of the rear discharge electrode 207 and isparallel to the front substrate 201, is considered. The horizontal axis(x-axis) intersects the lateral line 208 b of the first barrier rib 208at a first position P₁. Also, a virtual vertical axis (y-axis), which isorthogonal to the horizontal axis (x-axis) at the first position P₁,intersects the front substrate 201 at a second position P₂. In thiscase, a tangent angle θ, between a tangent line T and the vertical axis(y-axis) at the first position P₁ becomes a parameter that representsthe gradient of the lateral line 208 b.

FIG. 6 is a graph of a sustain voltage margin with respect to a tangentangle, and FIG. 7 is a graph of a thickness deviation of the MgO layerwith respect to a tangent angle.

Referring to FIG. 6, when a tangent angle θ is 13°, the sustain voltagemargin has a maximum of 15 V, and is generally distributed in a convexshape. When the tangent angle θ is less than 0° or more than 17°, thesustain voltage margin is greatly reduced. If an absolute value of thetangent angle θ is too great, a gradient is increased as much. Thisresults in a difference between the depths H₁ and H₂ of portions of thefirst barrier rib 208 that cover the front and rear discharge electrodes206 and 207 as described above. Consequently, the amount of wall chargeaccumulated on both of the electrodes 206 and 207 becomes differentduring discharge, thus causing non-uniform discharge.

In FIG. 7, the thickness deviation |A−B| of the MgO layer 209 refers toan absolute value of the difference between a thickness A of the MgOlayer 209, obtained at a third position (P₃ of FIG. 5), and a thicknessB of the MgO layer 209, obtained at a fourth position (P₄ of FIG. 5).Referring to FIG. 5, a virtual line which extends from a vertical centerP₅ of the rear discharge electrode 207 and is parallel to the horizontalaxis (x-axis) intersects the lateral line 208 b of the first barrier rib208 at the third position P₃. Also, a virtual line which extends from avertical center P₆ of the front discharge electrode 206 and is parallelto the horizontal axis (x-axis) intersects the lateral line 208 b of thefirst barrier rib 208 at the fourth position P₄.

Referring to FIG. 7, it can be observed that, as the tangent angle θdecreases, the thickness of the MgO layer 209 becomes more non-uniform,because the lateral line 208 b of the first barrier rib 208 is disposedin a more slanted orientation relative to the direction in which a MgOsource is emitted. Particularly, when the tangent angle θ is less than4°, the thickness deviation |A−B| of the MgO layer 209 increases.Accordingly, when the tangent angle θ is less than 4°, discharge isnon-uniformly generated and discharge properties are degraded.

Therefore, it is concluded from FIGS. 6 and 7 that the tangent angle θshould range from 4° to 17° in order to obtain a sufficient sustainvoltage margin and an MgO layer with a uniform thickness.

A method of driving the PDP 200 having the above-described structurewill now be described.

At the outset, by applying an address voltage between the addresselectrodes 203 and the rear discharge electrodes 207, address dischargeis induced, with the result that one discharge cell 220 on which sustaindischarge will be generated is selected.

Thereafter, if an alternating current (AC) sustain discharge voltage isapplied between the front discharge electrode 206 and the rear dischargeelectrode 207 of the selected discharge cell 220, sustain discharge isinduced between the front discharge electrodes 206 and rear dischargeelectrodes 207. As the energy level of a discharge gas excited by thesustain discharge is lowered, ultraviolet rays are emitted. Then, theultraviolet rays excite the phosphor layer 210 coated inside thedischarge cell 220. As the energy level of the excited phosphor layer210 is lowered, visible rays are emitted. The emitted visible rays forman image.

In the PDP 100 shown in FIG. 1, because sustain discharge ishorizontally generated between the scan electrodes 106 and the commonelectrodes 107, the discharge area is relatively narrow. On the otherhand, in the PDP 200 of the present invention, sustain discharge isgenerated from all of the lateral surfaces that define the dischargecell 220, and thus the discharge area is relatively wide.

Also, in the exemplary embodiment of the present invention, the sustaindischarge is induced in the form of a closed curve along the lateralsurfaces of the discharge cell 220, and then gradually spread toward thecenter of the discharge cell 220. Thus, the volume of a region where thesustain discharge occurs is increased. Moreover, even space charges ofthe discharge cell 220, which are not conventionally utilized,contribute to luminescence. As a result, the luminous efficiency of thePDP 200 is enhanced.

Furthermore, in the PDP 200 of the present invention, as shown in FIG.3, sustain discharge is generated only in portions defined by the firstbarrier ribs 208. Accordingly, unlike in the PDP 100, the ion-sputteringof the phosphor layers due to charged particles is prevented so that,even if the same image is displayed for a long period of time, nopermanent image sticking is caused.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetail may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A plasma display panel, comprising: a front substrate; a rearsubstrate disposed in opposition to the front substrate; first barrierribs disposed between the front substrate and the rear substrate fordefining discharge cells with the front substrate and the rearsubstrate, and formed of a dielectric material; front dischargeelectrodes disposed inside the first barrier ribs so as to surround thedischarge cells; rear discharge electrodes spaced apart from the frontdischarge electrodes and disposed inside the first barrier ribs so as tosurround the discharge cells; phosphor layers disposed in the dischargecells; and a discharge gas deposited in the discharge cells; wherein,from a longitudinal sectional view of the first barrier ribs, a virtualhorizontal axis extending from a lowermost portion of each of the reardischarge electrodes and parallel to the front substrate intersects alateral surface of the first barrier ribs at a certain position; andwherein an angle between a tangent line at an intersection of thehorizontal axis and the lateral surfaces of the first barrier ribs, onone side, and a virtual vertical axis orthogonal to the horizontal axis,on another side, ranges from 4° to 17°.
 2. The plasma display panel ofclaim 1, wherein the front discharge electrodes extend in a certaindirection, and the rear discharge electrodes extend in a direction whichcrosses the certain direction in which the front discharge electrodesextend.
 3. The plasma display panel of claim 1, wherein the frontdischarge electrodes and the rear discharge electrodes extend indirections which are parallel to each other; said plasma display panelfurther comprising address electrodes extending in such a direction asto cross the directions in which the front discharge electrodes and therear discharge electrodes extend.
 4. The plasma display panel of claim3, wherein the address electrodes are disposed between the rearsubstrate and the phosphor layers.
 5. The plasma display panel of claim3, further comprising a dielectric layer to cover the addresselectrodes.
 6. The plasma display panel of claim 1, further comprisingsecond barrier ribs which define the discharge cells with the firstbarrier ribs.
 7. The plasma display panel of claim 6, wherein thephosphor layers are disposed on lateral surfaces of the second barrierribs.
 8. The plasma display panel of claim 1, wherein each of the frontdischarge electrodes and each of the rear discharge electrodes has ashape of a ladder.
 9. The plasma display panel of claim 1, wherein atleast lateral surfaces of the first barrier ribs are covered byprotective layers.